1. Field of the Invention
The present invention relates to an apparatus and a method for cancelling co-channel interference. More particularly, the invention relates to a co-channel interference canceler and a method therefor, which reliably cancel co-channel interference in a high definition television (HDTV).
2. Description of the Related Art
Grand Alliance-Advanced Television (GA-ATV) is a new digital television transmission system standard capable of replacing the NTSC (National Television System Committee) standard. The GA-ATV system (also called "GA-HDTV" or "GAVSB") is standardized by the Advanced Television System Committee (ATSC) and adopts a vestigial side band (VSB) modulation method as a digital transmission method.
A new ATV signal is transmitted together with a conventional analog television signal (NTSC signal) via a television channel which is not in use in a given geographic region ("taboo" channel). Accordingly, a GA-ATV receiver must be designed to resist NTSC co-channel interference.
The block diagram of a conventional HDTV receiver is shown in FIG. 1, which is disclosed in U.S. Pat. No. 5,594,496.
An NTSC interference rejection filter (NRF) selection controller 110 of FIG. 1 may be constituted of a field comb filter, a comb filter and a comparator disclosed in the above patent, and may have a structure disclosed in the reference [1] "Guide to the use of the digital television standard for HDTV transmission", pp.104.about.107, Doc.A/54, submitted to the United States Advanced Television System Committee, Apr. 12, 1995, or may have another structure.
Here, when adopting the comb filter suggested by the above patent and ATSC standards as the NRF 108, performance in removing the NTSC interference signal is excellent.
However, since the comb filter subtracts two signals at full gain, the power of additive white Gaussian noise (AWGN) is increased by 3 dB, thereby causing a loss of signal-to-noise ratio (SNR) of 3 dB while passing through the comb filter. Also, the comb filter changes the 8-level input signal to a 15-level signal.
The NRF selection controller 110 of FIG. 1 generates a selection signal which selects the path with less error from a path (non-NRF path) which does not include the NRF 108 and a path (NRF path) including the NRF 108. The controller applies the result to a selector 112, an adaptive equalizer 114, a phase tracker 116 and a trellis decoder 118. The selector 112 selects the output signal (15-level) of the NRF 108 or the output signal (8-level) of a unit 106, according to the selection signal. The adaptive equalizer 114, the phase tracker 116 and the trellis decoder 118 properly process the selected signal.
Thus, the selection of the NRF 108 by the NRF selection controller 110 of the receiver shown in FIG. 1 is performed before the adaptive equalizer 114, the phase tracker 116 and the trellis decoder 118, which means that the input signal into the NRF selection controller 110 includes AWGN, ghost, phase noise, etc. as well as the co-channel interference signal. To solve this problem, according to the above patent, the input signal, including a field sync of successive fields, is comb-filtered by using a field comb filter to generate a subtraction signal from which static ghost, DC offset, symbol interference, etc. has been removed. The NRF is selected by comparing the comb-filtered subtraction signal with a subtraction signal which does not go through the comb filter, thereby removing the NTSC co-channel interference and other interference.
However, in the above patent, moving ghost or phase noise is not removed, so reliability in controlling selection of the NRF is still less than optimal.
On the other hand, as another conventional co-channel interference canceler, U.S. Pat. No. 5,546,132 discloses an NTSC interference detector using received data over all periods instead of a data field sync reference pattern. U.S. Pat. No. 5,602,583 discloses an NTSC interference rejection filter with a switched Tomlinson precoder for reducing the NTSC co-channel interference in the ATV receiver, and U.S. Pat. No. 5,325,188 discloses an NTSC signal interference canceler using digital recursive notch filters.